It is sometimes desirable to provide a fine feed position adjustment between members which are movable over a relatively great range of motion. This necessitates a disengagement of the mechanism to allow rapid movement of the members to reach the points where such fine adjustments are necessary.
As an example, in some types of coordinate measuring machines, an X-axis carriage member is mounted for movement along ways on a member of a Y-axis bridge which is in turn mounted on a supporting base member, so as to carry a probe along orthogonal X and Y axes to carry out measurements of objects supported on a table fixed to the base. The probe itself is also mounted for vertical or Z axis motion of the probe tip.
In lower cost versions of such machines, the carriage, bridge, and probe members are each moved manually along guide ways during measuring operations, and these members may be moved through a relatively great range of motion in moving the probe to reach particular features on the measured object.
It is desirable to have a fine feed mechanism for carrying out the final stages of probe movement along a given axis after it has been manually traversed to approach the point of interest on the measured object. Thus, in order to move these members along their respective support ways to quickly reach a point of interest on the object, such fine feed mechanisms must be disengageable to allow such manual motion.
In U.S. Pat. No. 3,817,111 issued on June 18, 1974, to Paul E. Allen, for a "LOCK AND TRAVERSE FINE FEED MECHANISM AND BEARING ARRANGEMENT FOR A MEASURING MACHINE CARRIAGE", there is disclosed a mechanism for accomplishing this result, but which requires relatively costly components, including a threaded shaft and brake bar each extending the full length of the travel of the carriage. The threaded shaft, being a separately supported member, may also sag excessively which sagging could interfere with proper operation if disposed horizontally, and thus must be of substantial diameter to be of sufficient rigidity. This increased size requirement increases the cost of the machine.
Since it is important that such fine feed mechanisms providing this capability be able to be manufactured at low cost an arrangement which did not require such substantial separate members would be advantageous.